Modeling granular hopper discharge and segregation for wet cohesive particles

The present work investigates hopper discharge phenomenon from a quasi-3D, rectangular hopper using the Discrete Element Method. Accurate prediction of the discharge rate from hoppers is important in many industrial processes involving the handling of granular materials. For cohesionless granular media, the effects of particle properties (particle size and size distribution) and hopper geometry (hopper width, outlet width, angle and fill height) are studied and compared to previously published experimental correlations. The results indicate that DEM simulations are fully capable of reproducing trends in the discharge rate that are well-known experimentally. For example, particle size and hopper width are shown to have a minimal influence on the discharge rate. In addition, for rectangular hoppers, the discharge rate is shown to vary with the outlet width raised to the 3/2 power as given by the modified Beverloo correlation. The DEM simulations are also used to explore a wider range of parameters that have not been or are not easily explored experimentally. For example, the effects of hopper friction, particle friction, and coefficient of restitution are investigated, and particle friction is shown to have a significant influence on the hopper discharge behavior.;The present work also investigates the parameters affecting the discharge rate of a wet cohesive system. The cohesion between the particles is described by a pendular liquid bridge force model and the strength of the cohesive bond is characterized by a Bond number. The Beverloo correlation is applied to cohesive systems by modifying the Beverloo constant as a function of Bond number. The predictions obtained from this modified correlation fit the simulation data reasonably well. In addition, the effect of hopper angle in cohesive systems is shown to follow a trend similar to cohesionless systems, where the discharge rate is insensitive to changes in hopper angle except below a critical angle (with respect to the vertical) where the discharge rate increases rapidly. This critical angle of flow decreases with increasing cohesion.;Granular materials may readily segregate due to differences in particle properties such as size, shape, and density. Segregation is common in industrial processes involving granular materials and can occur even after a material has been uniformly blended. One of the specific objectives of this work includes investigating via simulation the effect of particle cohesion due to liquid bridging on particle segregation. Specifically, a bi-disperse granular material flowing from a 3-D hopper is simulated using the discrete element method (DEM) for cohesive particles and the extent of discharge segregation is characterized over time. The strength of the cohesive bond is characterized by the Bond number determined with respect to the smaller particle species. As the Bond number of the system increases, the extent of discharge segregation in the system decreases. A critical value of Bo = 1 is identified as the condition where the primary mechanism of segregation in the cohesionless hopper system, i.e. gravity-induced percolation, is essentially eliminated due to the liquid bridges between particles.;Finally, experiments are performed in a hopper of identical dimensions as in the simulation to verify the model. Three specific characteristic of the flow: discharge rate, angle of repose of the material and size of clumps formed during the discharge are investigated experimentally and compared to the simulations. The simulation results agree well with the experimental results. In general, the discharge rate decreases, angle of repose increases and size of clumps increases as cohesion increases. (Full text of this dissertation may be available via the University of Florida Libraries web site. Please check http://www.uflib.ufl.edu/etd.html)...